This invention concerns a product which is provided with a coding pattern, which comprises a number of marks, each of which represents one of at least two different values. The invention also concerns use of such a coding pattern.
Storing coded information on a surface by means of different types of marks is already known.
U.S. Pat. No. 5,852,434 describes, for example, a position-coding pattern which codes X-Y-coordinates for a number of positions on a writing surface. The position-coding pattern makes it possible for a user to record electronically graphic information which is created on a writing surface by continuously reading the position-coding pattern.
Three examples of the construction of the position-coding pattern are given in U.S. Pat. No. 5,852,434. In the first example the pattern consists of symbols, each of which is constructed of three concentric circles. The outer circle represents the X-coordinate and the middle circle the Y-coordinate. Both the outer circles are additionally divided into 16 parts which, depending upon whether they are filled in or not, indicate different numbers. This means that each pair of coordinates X, Y is coded by a complex symbol with a particular appearance.
In the second example, the coordinates of each point on the writing surface are given by means of bar-codes, a bar-code for the X-coordinate being shown above a bar-code for the Y-coordinate.
A checkered pattern which can be used to code the X- and Y-coordinates is given as a third example. However, there is no explanation as to how the checkered pattern is constructed or how it can be converted into coordinates.
A problem with the known pattern is that it is constructed of complex symbols and the smaller these symbols are made, the more difficult it is to produce the patterned writing surface and the greater the risk of incorrect position determinations, while the larger the symbols are made, the poorer the position resolution becomes.
A further problem is that the processing of the detected position-coding pattern becomes rather complicated, due to the fact that a processor has to interpret complex symbols.
An additional problem is that the detector or sensor which is to record the position-coding pattern must be constructed in such a way that it can record four symbols at the same time so that it is certain to cover at least one symbol in its entirety, which is necessary in order for the position determination to be able to be carried out. The ratio between the required sensor surface and the surface of the position-coding pattern which defines a position is thus large.
In EP 0 578 692 a position-coding pattern is described which is constructed of cells in the form of squares. The value of the cells is determined by their appearance, for example their color. The cells can be separated by separation zones so that two adjacent cells with the same color can be distinguished. The position-coding pattern differs from that according to U.S. Pat. No. 5,852,434 in that a particular number of cells, that is symbols, together code a position. The coding is in addition floating, which means that an arbitrary partial surface of the pattern which contains the above-mentioned number of cells codes a position. Each cell thus contributes to the coding of several positions. In this way the ratio between the required sensor surface and the part of the position-coding pattern which defines a position is less than in the above-mentioned US patent. In addition each cell is less complex and therefore the processor which is to decode the position-coding pattern needs to be able to recognize fewer different elements. However, the processor needs to be able to locate and distinguish at least two different cells.
EP 0 171 284 B1 shows another floating position-coding pattern which is constructed of horizontal and vertical lines, the vertical lines coding the position in the horizontal direction and the horizontal lines coding the position in the vertical direction. The lines can be found in positions which are a multiple of 1 mm. The presence of a line in such a position codes a one (1), the absence of a line in such a position codes a zero (0).
It is, however, difficult to record and decode a pattern of lines, as the intersections between the lines can be difficult to record. In addition, it is often the case that the sensor is not held parallel to the base, which results in a perspective where the lines are no longer parallel. It can then be difficult to determine whether a line is actually missing. In addition, there must not be too many missing consecutive lines, as difficulties can then arise in the decoding. Furthermore, the information content is small.
Applicant""s Swedish Patent Application SE 9901954-9, which was filed on May 28, 1999 and which was not publicly available at the time of filing the present application and thereby does not constitute prior art, describes an additional position-coding pattern of the floating type in which the position-information is coded graphically by means of dots of a first and a second size, a dot of the first size corresponding to a zero (0) and a dot of the second size corresponding to a one (1). A plurality of dots together code the coordinates for a position.
It is a general desire that coding patterns which are used to store information on a surface must be able to code a lot of information per unit area and must be simple to detect and decode even when subjected to interference of difference kinds.
An object of the present invention is therefore to provide a product with a coding pattern which fulfils this requirement to at least as great an extent as the known coding patterns.
This object is achieved by means of a product according to claim 1.
The invention concerns more specifically a product which is provided with a coding pattern, which comprises a plurality of marks, each of which represents one of at least two different values. The coding pattern comprises a plurality of nominal positions, each of said marks being associated with one of said plurality of nominal positions and the value of each mark being determined by its location relative to its nominal position.
In prior art the coding is usually carried out by means of the appearance of one or more symbols or marks, the value of each symbol or mark being determined by its appearance. The device which decodes the coding pattern must consequently be able to recognize different symbols or marks, which increases the sensitivity to interference and makes the decoding more difficult.
According to the present invention, the value of each mark is determined instead by how it is located relative to its nominal position. As the value is based on the location of the mark, all the marks can have an identical appearance. The coding pattern is consequently simple to apply on the product. Furthermore, the detection of the marks is simple to carry out and unaffected by the presence of other marks on the product which are not part of the coding pattern. In addition, the coding pattern can be realized more simply using other technology than optical technology, for example as a chemical, electrical or mechanical pattern. The design of the mark also means that a product which is provided with a coding pattern will be more esthetically pleasing when the mark is optically readable. Finally, it is possible to have a large distance between the marks in relation to the density of the information, which means that the coding pattern is less sensitive to motion blur which can arise during the reading.
By nominal position is meant in this connection a position which is detectable and relative to which the mark can be located in different ways. The nominal positions can be marked on the product, but they can also be virtual and detectable indirectly.
It should also be pointed out that the value which a mark represents is preferably a numerical value, but can also be a character value, such a letter or some kind of symbol.
The location of the mark can preferably be determined by its center of gravity, which makes possible the use of marks of irregular shape and reduces the demands when applying the pattern on the product.
In a preferred embodiment, each nominal position is allocated a mark. The advantage is hereby obtained that all values are coded by a mark. The absence of a mark thus always constitutes an error.
The marks can be placed both in the nominal position and outside the same. A possible representation of a binary pattern could, for example, be that a mark in the nominal position represents a zero and a mark outside the nominal position represents a one, or vice versa.
In a preferred embodiment, however, essentially all the marks are displaced relative to their nominal position. In this way the pattern is random, while at the same time it is so uniform that it appears even to the eye.
A few marks should, however, be able to be in their nominal position in order to indicate some specific parameters, for example the position of the virtual raster.
In addition, in a preferred embodiment, essentially all the marks are displaced the same distance relative to their nominal position. If it is known where the nominal position is located, it is sufficient to look for a mark at a certain distance from the nominal position, which facilitates the locating of the marks and reduces the risk of errors. In addition, it is sufficient to detect that there is a mark at the relevant distance from the nominal position. The appearance of this mark is of subordinate significance, which reduces the need for precision in applying the pattern on the product.
In a particularly preferred embodiment, each mark is displaced in one of four orthogonal directions relative to its nominal position. By knowing the nominal position the mark accordingly only needs to be looked for in four different directions. This facilitates and speeds up the locating of the marks. In addition, it reduces the risk of errors, as marks which are not part of the pattern and which are situated in other positions than along the four orthogonal directions are not detected and thereby do not run the risk of affecting the decoding of the pattern.
In order for it to be possible to determine the locations of the marks relative to the nominal positions, the nominal positions must be known. For this purpose the coding pattern preferably comprises a raster with raster lines, where the intersections of the raster lines define the nominal positions of the marks. The nominal positions are thus regularly arranged on the product. This facilitates the detection and reduces the risk of error. In addition, it makes possible the use of a virtual raster.
In a preferred embodiment, the distance between the raster lines is approximately 250 xcexcm to 300 xcexcm, preferably 300 xcexcm. This makes possible a high density of information, but still with reliable detection.
In a preferred embodiment, the raster lines also form a rectangular, preferably square, grid. In the latter case, the distance between the raster lines is thus the same in both directions.
In a preferred embodiment, each mark is additionally displaced along one of the raster lines. When the raster is known, the marks can thus be located in an efficient way by searching along the well-defined directions which the raster lines represent.
In a preferred embodiment, each mark is displaced from its nominal position by a distance which is xc2xc to xe2x85x9, preferably ⅙, of the distance between the raster lines. If the displacement is approximately ⅙ of the raster line interval, it is relatively easy to determine to which nominal position the mark belongs. If the displacement is less than approximately xe2x85x9, it can be difficult to detect, that is the resolution requirement is too great. If the displacement is more than approximately xc2xc, it can be difficult to determine to which nominal position the mark belongs. This applies in particular if the representation of the coding pattern recorded by the sensor or detector is distorted, which for example can occur if an optical sensor is held at an angle relative to the surface on which the coding pattern is arranged. With the above-mentioned preferred raster line interval of 300 xcexcm, the preferred displacement is thus 50 xcexcm.
The raster with the raster lines can be indicated on the surface in such a way that it can be read directly by the device which detects the marks. In this case, however, the raster must also be able to be detected by the device and distinguished from the marks. In a preferred embodiment, the raster is instead virtual, which means that it is not marked on the product in any way, but can be located from the locations of the marks. Instead of being read from the product, it is thus determined indirectly by means of the marks.
As already mentioned, essentially all the marks in a preferred embodiment have an essentially identical appearance. This makes it simpler to arrange them on the product.
The marks have preferably some simple geometric shape. They are thus advantageously approximately circular, triangular or rectangular. They can be filled-in or not, but the former is preferable as detection is then simpler.
The mark should not cover its nominal position and should therefore not have a larger diameter than twice the displacement, that is 200%. This is, however, not critical, as a certain amount of overlapping is permissible, for example 240%. The smallest size is determined in the first place by the resolution of the sensor and the requirements of the printing process used to produce the pattern. However, in practice the marks should not have a smaller diameter than approximately 50% of the displacement, in order to avoid problems with particles and noise in the sensor.
The coding pattern can be realized with any parameters which can be used to produce marks of the above-mentioned type which can be detected by a detector. The parameters can be electrical or chemical or of some other type. The coding pattern is, however, preferably optically readable in order for it to be simpler to arrange on the product. It can, for example, be printed on the product.
In a preferred embodiment, the coding pattern is readable by infrared light. In this way information which is not readable by infrared light can be overlaid on the coding pattern without interfering with the reading of this.
In a preferred embodiment, the marks constitute 0.25% to 20%, preferably approximately 9%, of the surface which is taken up by the coding pattern. If the pattern is printed, for example, on a sheet of white paper, it will in this case only result in a pale gray shading of the paper, which means that it will appear as essentially normal paper.
The coding pattern is preferably a position-coding pattern which codes a plurality of positions on the product, each position being coded by means of a plurality of marks. The coding pattern can, however, also be used to code other information.
The product can be any product which can be provided with a coding pattern. It does not need to be a physical product, but can also be electronic, for example an image or a surface on a computer screen on which the coding pattern is overlaid in electronic form.
According to another aspect of the invention, this concerns use of a coding pattern which comprises a plurality of marks, each of which represents one of at least two different values, and a plurality of nominal positions, each of said plurality of marks being associated with one of said plurality of nominal positions and the value of each mark being determined by its location relative to its nominal position.
The advantages of the use of such a pattern are apparent from the discussion of the coding pattern on the product. The features which are mentioned for the coding pattern on the product also apply, of course, to the use of the coding pattern. The use can, for example, consist of printing out the coding pattern on a product, storing the coding pattern in electronic form or decoding the coding pattern.